Gyroscopes present the dominant source of navigational error in inertial navigation systems. In the most severe case, a failed gyroscope can render the navigational system completely inoperative. In all cases, navigational errors occur which are directly related to drift or bias changes in the system gyroscopes since the last calibration. Accordingly, the gyroscopes comprising the navigation system must be initially calibrated and periodically re-calibrated to account for the gyroscopes' drift over time.
If a high degree of navigational accuracy is desired, costly high performance gyroscopes having small bias drift uncertainties are used. To achieve the desired performance, gyroscopes are mounted on a gimballed platform that is used to implement a multiposition calibration. Neither solution may be attractive or even contemplated due to gyroscope cost considerations and/or gimbal configuration penalties. For example, total navigation system cost may prohibit the use of the more costly high-performance gyroscopes; while the implementation of a gimballed platform for calibrating gyroscopes is expensive, and results in considerable additional volume, weight and complexity. Further, when the vehicle is navigating, complex vehicle maneuvers and external aids as well as the additional computation complexity for the implementation of a Kalman filter are required for calibration of the gyroscopes. Additionally, the gimballed platform calibration process is very time consuming and may take up to 40 minutes to perform before the vehicle's inertial navigation system is capable of providing the desired navigational accuracy. Most importantly, during gyroscope calibration or re-calibration, the navigational functions of the inertial navigation system must be temporarily suspended.